Fluorine-containing polymers and preparation thereof

ABSTRACT

A method for polymerizing fluorine-containing ethylenically-unsaturated monomer and allylic-hydrogen containing olefin monomer is provided. The method involves the use of fluoroaliphatic-group containing sulfinate. Novel polymers are also disclosed, comprising interpolymerized units derived from tetrafluoroethylene and allylic-hydrogen containing olefin, for example, propylene.

This is a division of application Ser. No. 08/355,506 filed Dec. 14,1994, abandoned.

FIELD OF THE INVENTION

This invention relates to fluorine-containing polymers, theirpreparation and use. In another aspect, this invention relates tomethods of flee-radical polymerization of monomer mixtures comprising afluorine-containing ethylenically-unsaturated monomer and anallylic-hydrogen containing olefin monomer, and to the resultingpolymers and shaped articles thereof.

BACKGROUND OF THE INVENTION

Fluorine-containing polymers, or fluoropolymers, are an important classof polymers and include for example, amorphous fluorocarbon elastomersand semi-crystalline fluorocarbon plastics. Within this class arepolymers of high thermal stability and usefulness at high temperatures,and extreme toughness and flexibility at very low temperatures. Many ofthese polymers are almost totally insoluble in a wide variety of organicsolvents, and are chemically inert. Some have extremely low dielectricloss and high dielectric-strength, and most have unique nonadhesive andlow-friction properties. See, for example, F. W. Billmeyer, Textbook ofPolymer Science, 3rd ed., pp. 398-403, John Wiley & Sons, New York(1984).

Amorphous fluorocarbon elastomers, particularly the copolymers ofvinylidene fluoride with other ethylenically unsaturated halogenatedmonomers, such as hexafluoropropene, have particular utility in hightemperature applications, such as seals, gaskets, and linings--see, forexample, Brullo, R. A., "Fluoroelastomer Rubber for AutomotiveApplications," Automotive Elastomer & Design, June 1985,"Fluoroelastomer Seal Up Automotive Future," Materials Engineering,October 1988, and "Fluorinated Elastomers," Kirk-Othmer, Encyclopedia ofChemical Technology, Vol. 8, pp. 500-515 (3rd ed., John Wiley & Sons,1979).

Semi-crystalline fluoroplastics, particularlypolychlorotrifluoroethylene, polytetrafluoroethylene, copolymers oftetrafluoroethylene and hexafluoropropylene, and poly(vinylidenefluoride), have numerous electrical, mechanical, and chemicalapplications. Fluoroplastics are useful, for example, in wire coatings,electrical components, seals, solid and lined pipes, and pyroelectricdetectors. See, for example, "Organic Fluorine Compounds," Kirk-Othmer,Encyclopedia of Chemical Technology, Vol. 11, pp. 20, 21, 32, 33, 40,41, 48, 50, 52, 62, 70, 71, John Wiley & Sons, (1980).

Fluorine-containing polymers can be prepared by free-radical initiatedpolymerization of one or more fluorine-containing ethylenicallyunsaturated monomers. Free radicals are typically formed by thedecomposition of a free-radical initiator. Free-radical initiators maybe decomposed by light, heat, high energy radiation, or as a result ofoxidation-reduction reactions. When free radicals are generated in thepresence of free-radical polymerizable ethylenically unsaturatedmonomers, a chain reaction occurs producing polymer. The polymer can beprepared by polymerization of monomers in bulk, in solution, inemulsion, or in suspension. Fluoroelastomers and fluoroplastics arepreferably prepared by aqueous emulsion or suspension polymerizationbecause of the rapid and nearly complete conversion of monomers, easyremoval of the heat of polymerization and ready isolation of thepolymer. Emulsion or suspension polymerization typically involvespolymerizing monomers in an aqueous medium in the presence of aninorganic free-radical initiator system, and surfactant or suspendingagent.

Copolymers of tetrafluoroethylene ("TFE") and propylene, and terpolymersof TFE, propylene, and vinylidene fluoride are known and usefulpolymers. See, e.g., D. E. Hull et al., "New Elastomers are MoreResistant to Many Automotive Fluids," SAE Technical Paper Series,#890361, SAE Publications Division, Warrendale, Pa., (1989), D. E. Hullet al., "New Type Fluoroelastomers With Improved Chemical Resistance toAutomotive Oils and Lubricants," SAE Technical Paper Series, #900121,SAE Publications Division, Warrendale, Pa., (1989), Grootaert et al.,"Elastomers, Synthetic Fluorocarbon Elastomers," Kirk-Othmer,Encyclopedia of Chemical Technology, Fourth Ed., Vol. 8, pp. 990-1005,John Wiley & Sons, (1993), Grootaert et al., "A Novel FluorocarbonElastomer For High-Temperature Sealing Applications In AggressiveMotor-Oil Environments," Rubber Chemistry and Technology, Volume 63, pp.516-522, American Chemical Society (1990), and Kolb et al., "AgingBehavior of Fluorocarbon in Various Motor Oils," Automotive Polymers &Design, Volume 7 (No. 6), pp. 10-13, Lippincott & Peto, Inc. (1988).However, their manufacture has been known to be difficult, particularlywith respect to the preparation of amorphous polymers derived from TFEand propylene. Various patents describe processes to make thesepolymers.

U.S. Pat. No. 3,859,259 (Harrel et al.) prepares certain amorphouscopolymers of TFE and propylene by a continuous aqueous emulsionpolymerization process at high pressure (preferably about 500 to 1,500psig) using ammonium persulfate as initiator and sodium lauryl sulfateas the emulsifier.

U.S. Pat. No. 5,037,921 (Carlson) prepares certain fluoroelastomercopolymers of TFE and propylene by a semi batch, emulsion polymerizationprocess in the presence of diiodo chain transfer agents. Thepolymerizations are preferably run at temperatures of 70° C. to 90° C.and preferably at pressures of 2.6 to 2.7 MPa (380 to 400 psig).

U.S. Pat. No. 3,933,773 (Foerster) prepares certain thermoplasticelastomeric copolymers of TFE and propylene by an emulsionpolymerization reaction utilizing a redox initiator system at a pressureof 100 to 1,000 psig, preferably 250 to 350 p.s.i.g.

It is generally believed that one important problem in thesepolymerizations is degradative chain transfer reactivity ofalpha-olefins containing an allylic hydrogen, e.g., propylene. See,e.g., Encyclopedia of Polymer Science and Engineering, Volume 13, pp.714-715, John Wiley & Sons (1988), and George Odian, Principles ofPolymerization, 2nd Ed., pp. 250-251, John Wiley & Sons. Thisdegradative chain transfer is thought to be due to the weakness of theallylic carbon-hydrogen bond. For example, in propylene polymerizations,it is thought that a propylene molecule reacts with a propagatingpolymer-chain radical through transfer of its allylic hydrogen insteadof through its double bond thus leading to low polymerization rates andresulting in polymers with low molecular weight. The formed allylradical is resonance stabilized and unable to initiate a newpolymerization. ##STR1## This reaction is also believed to betemperature dependent, and the polymerization rate is expected todecrease at higher temperatures. Therefore a great deal of effort hasbeen put into development of low temperature redox initiating systemsthat would allow fast reaction rates and high molecular weightcopolymers. Note that other monomers such as methyl methacrylate andmethacrylonitrile, which also contain allylic carbon-hydrogen bonds, donot under go extensive degradative chain transfer because the ester ornitrile substituents are believed to stabilize the propagating radicalsand decrease their reactivity toward transfer compared to olefins.

U.S. Pat. No. 4,277,586 (Ukihashi et al.) discloses a method for the lowtemperature (0°-50° C.) polymerization of TFE and propylene. The patentstates in Col. 1 that "propylene-tetrafluoroethylene copolymers preparedby the conventional processes are characterized by low molecular weight. . . " In the method of the '586 patent "When the reaction temperatureis above 50 ° C., the molecular weight of the copolymer will bedecreased and the Mooney viscosity of the copolymer will be increased."(Col. 3, line 68, and Col. 4, lines 1-3). See also, G. Kojima and M.Hisasue, "Die Emulsionscopolymerisation yon Tetrafluoroethylen mitPropylen bei niedrigen Temperaturen," Makromol. Chem., Vol. 182, pp.1429-1439 (1981).

In U.S. Pat. No. 4,463,144 (Kojima et al. ) this process was improved bymeans of an initiating system comprising a water soluble persulfate, awater soluble iron salt, a hydroxymethanesulfinate, andethylenediaminetetraacetic acid or a salt thereof, in an alkalineaqueous solution containing a specific amount of tertiary butanol and anemulsifier at pH of up to 10.5. The tertiary butanol is said to act asan accelerator and "If the amount of tertiary butanol is less than 5 wt.%, no adequate effects are obtainable." (Col. 4, lines 5-7).

U.S. Pat. No. 5,285,002 (Grootaert) discloses the preparation offluorine-containing polymers by polymerizing an aqueous emulsion orsuspension of a polymerizable mixture comprising fluoroaliphatic-groupcontaining sulfinate.

SUMMARY OF THE INVENTION

Briefly, in one aspect, the present invention provides a method for thepreparation of fluorine-containing polymer comprising polymerizing,under free-radical conditions, an aqueous emulsion or suspension of apolymerizable mixture comprising a fluorine-containingethylenically-unsaturated monomer, an allylic-hydrogen containing olefinmonomer, e.g., propylene, a fluoroaliphatic-group containing sulfinate,and an oxidizing agent capable of oxidizing said sulfinate to a sulfonylradical.

In another aspect, this invention provides semi-crystalline copolymerscomprising interpolymerized units derived from TFE and allylic-hydrogencontaining olefin monomer, e.g., propylene, wherein less than 10%,preferably less than 5%, of the total heat of fusion is attributable toa secondary melt-transition above 300° C. as shown by the heating curvefrom Differential Scanning Calorimetry (DSC). The resulting polymerspossess improved processing compared to prior art polymers, particularlyat low processing temperatures.

We have found that with the use of the initiating system disclosed inU.S. Pat. No. 5,285,002, supra,, both redox and thermal initiation ispossible for monomer mixtures containing fluorine-containing monomersand allylic-hydrogen containing monomers. Compared to prior artprocesses, particularly in the preparation of amorphous polymers, theprocess of the present invention does not require cosolvents such astertiary butanol, can be run smoothly at relatively low pressures, andproceeds at relatively rapid reaction rates. The polymers obtained areof usable molecular weight as indicated by their viscosity or melt-flowindex (MFI) which are in the range of viscosities or MFI generally seenin commercially useful polymers, and are clean colorless polymers.Furthermore, there is no evidence of the degradative chain transfer,even when polymerized at elevated temperatures such as 71° C., asevidenced by the absence of a detectable CF₂ H resonance in the protonNMR.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 through 5 show heating curves from Differential ScanningCalorimetry (DSC) for the polymers prepared in Examples 6-8 andComparative Examples C3 and C4, infra.

DETAILED DESCRIPTION OF THE INVENTION

A class of the fluoroaliphatic sulfinates useful in this invention canbe represented by the following general formulae ##STR2## wherein R_(f)represents a monovalent fluoroaliphatic group having, for example, from1 to 20 carbon atoms, preferably 4 to 10 carbon atoms, R_(f) 'represents a polyvalent, preferably divalent, fluoroaliphatic grouphaving, for example, from 1 to 20 carbon atoms, preferably from 2 to 10carbon atoms, M represents a hydrogen atom or cation with valence x,which is 1 to 2, and is preferably 1, n is 2 to 4, preferably 2.

The monovalent fluoroaliphatic group, R_(f), is a fluorinated, stable,inert, non-polar, saturated moiety. It can be straight chain, branchedchain, and, if sufficiently large, cyclic, or combinations thereof, suchas alkyl cycloaliphatic groups. Generally, R_(f) will have 1 to 20carbon atoms, preferably 4 to 10, and will contain 40 to 83 weightpercent, preferably 50 to 78 weight percent fluorine. The preferredcompounds are those in which the R_(f) group is fully or substantiallycompletely fluorinated, as in the case where R_(f) is perfiuoroalkyl,C_(n) F_(2n+1), where n is 1 to 20.

The polyvalent, preferably divalent, fluoroaliphatic group, R_(f) ', isa fluorinated, stable, inert, non-polar, saturated moiety. It can bestraight chain, branched chain, and, if sufficiently large, cyclic orcombinations thereof, such as alkyl cycloaliphatic divalent groups.Generally, R_(f) ', will have 1 to 20 carbon atoms, preferably 2 to 10.Examples of preferred compounds are those in which the R_(f) ' group isperfluoroalkylene, C_(n) F_(2n), where n is 1 to 20, orperfluorocycloalkyl, C_(n) F_(2n-2), where n is 5 to 20.

With respect to either R_(f) or R_(f) ', the skeletal chain of carbonatoms can be interrupted by divalent oxygen, hexavalent sulfur ortrivalent nitrogen hereto atoms, each of which is bonded only to carbonatoms, but preferably where such hetero atoms are present, such skeletalchain does not contain more than one said hetero atom for every twocarbon atoms. An occasional carbon-bonded hydrogen atom, iodine,bromine, or chlorine atom may be present; where present, however, theypreferably are present not more than one for every two carbon atoms inthe chain. Where R_(f) or R_(f) ' is or contains a cyclic structure,such structure preferably has 6 ring member atoms, 1 or 2 of which canbe said hetero atoms, e.g., oxygen and/or nitrogen. Examples of R_(f)groups are fluorinated alkyl, e.g., C₄ F₉ -, C₆ F₁₃ -, C₈ F₁₇ -,alkoxyalkyl, e.g., C₃ F₇ OCF₂ -. Examples of R_(f) ' are fluorinatedalkylene, e.g., -C₄ F₈ -, -C₈ F₁₆ -. Where R_(f) ' is designated as aspecific group, e.g., C₈ F₁₇ -, it should be understood that this groupcan represent an average structure of a mixture, e.g., C₆ F₁₃ - to C₁₀F₂₁ -, which mixture can also include branched structures.Representative fluoroaliphatic sulfinate compounds useful in thepractice of this invention include the following:

    CF.sub.3 SO.sub.2 Na

    C.sub.4 F.sub.9 SO.sub.2 H

    C.sub.4 F.sub.9 SO.sub.2 Na

    C.sub.6 F.sub.13 SO.sub.2 Na

    C.sub.8 F.sub.17 SO.sub.2 Na

    CF.sub.3 C(Cl).sub.2 CF.sub.2 SO.sub.2 K

    Cl(CF.sub.2).sub.8 OC.sub.2 F.sub.4 SO.sub.2 Na

    Cl(CF.sub.2).sub.x CF.sub.2 SO.sub.2 Na

where x is 1 to 10

    NaO.sub.2 SC.sub.8 F.sub.16 SO.sub.2 Na

    NaO.sub.2 Sc.sub.6 F.sub.12 SO.sub.2 Na

    NaO.sub.2 SC.sub.2 F.sub.4 OC.sub.2 F.sub.4 SO.sub.2 Na

    NaO.sub.2 SC.sub.2 F.sub.4 OC.sub.2 F.sub.4 X,

where X is br or I

    NaO.sub.2 S(C.sub.4 F.sub.8 O).sub.n C.sub.3 F.sub.6 SO.sub.2 Na

where n is 1 to 20

    NaO.sub.2 SCF.sub.2 O(CF.sub.2 CF.sub.2 O).sub.m (CF.sub.2 O).sub.n CF.sub.2 SO.sub.2 Na

where n and m are each 1 to 20

    (CF.sub.3).sub.2 NCF.sub.2 CF.sub.2 SO.sub.2 Na

    (C.sub.2 F.sub.5).sub.2 NCF.sub.2 CF.sub.2 SO.sub.2 Na

    N(C.sub.2 F.sub.4 SO.sub.2 Na).sub.3

    NaO.sub.2 SC.sub.8 F.sub.16 SO.sub.2 F

    NaO.sub.2 SC.sub.3 F.sub.6 O(C.sub.4 F.sub.8 O).sub.n C.sub.3 F.sub.6 SO.sub.2 Na

where n is 4 to 8 ##STR3##

Suitable fluorine-containing ethylenically-unsaturated monomers for usein this invention include the terminally unsaturated mono-olefinstypically used for the preparation of fluorine-containing polymers suchas vinylidene fluoride, hexafluoropropene, chlorotrifluoroethylene,2-chloropentafluoropropene, perfluoroalkyl vinyl ethers, e.g., CF₃OCF═CF₂ or CF₃ CF₂ CF₂ OCF═CF₂, tetrafluoroethylene,1-hydropentafluoropropene, 2-hydropentafluoropropene,dichlorodifluoroethylene, trifluoroethylene, 1,1-dichlorofluoroethylene,vinyl fluoride, and mixtures thereof. Perfluoro-1,3-dioxoles may also beused. The perfluoro-1,3-dioxole monomers and their copolymers aredescribed, for example, in U.S. Pat. No. 4,558,141 (Squire). Certainfluorine-containing di-olefins are also useful, such as,perfluorodiallylether and perfluoro-1,3-butadiene.

A class of the allylic-hydrogen containing olefin monomers useful inthis invention are those mono-olefins which contain only carbon,hydrogen, and halogen atoms. Suitable allylic-hydrogen containing olefinmonomers useful in the method of this invention include propylene,butylene, isobutylene, and 1,1,2-trifluoropropene.

The monomer mixtures useful in this invention may also containadditional ethylenically unsaturated comonomers, e.g., ethylene orbutadiene. Said monomer mixtures may also contain iodine- orbromine-containing cure-site comonomers in order to prepare peroxidecurable polymers, e.g., fluoroelastomers. Suitable cure-site monomersinclude terminally unsaturated mono-olefins of 2 to 4 carbon atoms suchas bromodifluoroethylene, bromotrifluoroethylene, iodotrifluoroethylene,CF₂ ═CFOCF₂ CF₂ Br, and 4-bromo-3,3,4,4-tetrafluorobutene-1.

The method of this invention can comprise otherwise conventionalemulsion or suspension free-radical polymerization techniques. Suchconventional emulsion or suspension polymerization techniques typicallyinvolve polymerizing monomers in an aqueous medium in the presence of aninorganic free-radical initiator system and surfactant or suspendingagent. In one aspect, the method of this invention comprises the use offluorinated suIfinate as a reducing agent and a water soluble oxidizingagent capable of converting the sulfinate to a sulfonyl radical.Preferred oxidizing agents are sodium, potassium, and ammoniumpersulfates, perphosphates, perborates, and percarbonates. Particularlypreferred oxidizing agents are sodium, potassium, and ammoniumpersulfates. The sulfonyl radical so produced is believed to eliminateSO₃, forming a fluorinated radical that initiates the polymerization ofthe monomers.

In addition to the sulfinate, other reducing agents can be present, suchas sodium, potassium or ammonium sulfites, bisulfite, metabisulfite,hyposulfite, thiosulfite, phosphite, sodium or potassium formaldehydesulfoxylate or hypophosphite. Activators such as ferrous, cuprous, andsilver salts, may also be present.

Aqueous emulsion and suspension polymerizations can be carried out underconventional steady-state conditions in which, for example, monomers,water, surfactants, buffers and catalysts are fed continuously to astirred reactor under optimum pressure and temperature conditions whilethe resulting emulsion or suspension is removed continuously. Analternative technique is batch or semibatch polymerization by feedingthe ingredients into a stirred reactor and allowing them to react at aset temperature for a specified length of time or by chargingingredients into the reactor and feeding the monomer into the reactor tomaintain a constant pressure until a desired amount of polymer isformed.

The amount of fluoroaliphatic sulfinate used can vary, depending, forexample, on the molecular weight of polymer desired. Preferably theamount of fluoroaliphatic sulfinate is from 0.01 to 50 mole %, and mostpreferably from 0.05 to 10 mole %, of sulfinate compound based on totalquantity of monomers.

Combinations of monosulfinates, disulfinates, and trisulfinates can beused, depending on whether it is desired to use sulfinate as aninitiator, a monomer, or both. When polyvalent sulfinates, such as thoserepresented by Formula II, are used, the sulfinate is believed to act asa monomer and the fluorinated moiety is believed to be incorporated intothe polymer backbone. When monosulfinates are used the fluorinatedmoiety is believed to be incorporated as a polymer end group.

Polymers prepared by the method of this invention, such as amorphousfluoroelastomers, can be compounded and cured using conventionalmethods. Such polymers are often cured by nucleophiles such as diaminesor polyhydroxy compounds. For example, certain fluoroelastomers preparedby the method of this invention may be crosslinked with aromaticpolyhydroxy compounds, such as bisphenols, which are compounded with thepolymer along with a curing accelerator, such as a quaternaryphosphonium salt, and acid acceptors, such as magnesium oxide andcalcium hydroxide. Particularly useful polyhydroxy compounds include4,4'-thiodiphenol, isopropylidene-bis(4-hydroxybenzene), andhexafluoroisopropylidene-bis(4-hydroxybenzene) ("bisphenol AF") whichare described, for example, in U.S. Pat. No. 4,233,421 (Worm). Suchcrosslinking methods are described, for example, in U.S. Pat. Nos.4,287,320 (Kolb), 4,882,390 (Grootaert et al.), 5,086,123 (Guenthner etal.), and Canadian Patent 2056692 (Kruger et al.).

Certain polymers may be cured with peroxides. A cure-site monomersusceptible to free-radical attack is generally required to renderpolymers peroxide-curable. For example, polymers which containinterpolymerized units derived from iodine- or bromine-containingmonomers are often peroxide-curable. Such cure-site monomers aredescribed, for example, in U.S. Pat. Nos. 4,035,565 (Apotheker et al.),4,450,263 (West), 4,564,662 (Albin), and Canadian Pat. Application No.2,056,692 (Kruger et al.)

The semi-crystalline polymers of this invention compriseinterpolymerized units derived from TFE and an allylic-hydrogencontaining olefin monomer. The semi-crystalline polymers of thisinvention differ from those of the prior art in that they exhibit a muchsmaller, high-temperature melt-peak. This is demonstrated by DSC curveswhich show that in the polymers of this invention, less than 10%,preferably less than 5%, most preferably less than 3%, of the total heatof fusion is attributable to a secondary melt-transition above 300° C.The semi-crystalline polymers of this invention possess improvedprocessing compared to prior art polymers, particularly at lowprocessing temperatures, i.e., at or below 300° C.

Fillers can be mixed with the polymers of this invention to improvemolding characteristics and other properties. When a filler is employed,it can be added in amounts of up to about 100 parts per hundred parts byweight of polymer, preferably between about 15 to 50 parts per hundredparts by weight of the polymer. Examples of fillers which may be usedare thermal-grade carbon blacks, or fillers of relatively lowreinforcement characteristics such as clays and barytes.

The sulfinate compounds useful in this invention result in polymerswhich have non-polar, non-ionic end groups. These non-ionic end groupsgenerally result in improved properties such as improved thermalstability and improved rheological behavior. Polymers with non-ionic endgroups exhibit lower apparent viscosities during processing, e.g.injection molding, when compared at the same shear rates to polymerswith ionic end groups. The resulting polymers may be elastomers orplastics. The polymers may be shaped to form useful articles includingO-rings, fuel-line hoses, shaft seals, and wire insulation.

EXAMPLES

In the following Examples and Comparative Examples polymers wereprepared. The average reaction rates were observed and calculated ingrams of total monomer consumed per liter of water (or water andcosolvent mixture) charged to the reactor per hour ("g/l-h").

Mooney Viscosities of polymers were measured at 12° C. according to ASTMD 1646-81, using a Monsanto Mooney Viscometer model MV 2000, a largerotor, 1 minute preheat, and measurement after 10 minutes "ML 1+10@121°C.").

MFI for polymers were obtained under the conditions described in theExamples and Comparative Examples using the methodology described inASTM D-1238 using a Tinius Olsen extrusion plastometer.

Thermal analysis was performed using a TA Instruments DSC-2910 and2000-series controller equipped with an LNCA-II controlled coolingaccessory. Heating curves were obtained under nitrogen purge byequilibrating samples at -100° C., holding isothermal for 1 minute,heating to 350° C. at a heating rate of 10° C. per minute, slowlycooling back to -100° C. under the "equilibrating segment" of theequipment software, and heating again to 350° C. at a heating rate of10° C. per minute. Heating curves shown in all of the Figures are fromthe second heating cycle.

Unless otherwise indicated, all % are by weight.

Preparation of sulfinates

Fluorochemical sulfinates can be prepared by deiodosulfination of thecorresponding iodides following the general procedure of Hu et al. in J.Org. Chem., Vol. 56, No. 8, 1991, page 2803. The fluorochemicalsulfinates C₄ F₉ SO₂ Na and C₆ F₁₃ SO₂ Na were prepared by reduction ofthe corresponding sulfonyl fluorides C₄ F₉ SO₂ F and C₆ F₁₃ SO₂ F withNa₂ SO₃ in a one to one mixture of water and dioxane. See also, U.S.Pat. No. 5,285,002, supra. The purity of these fluorochemicalsulfinates, as determined by ¹⁹ F NMR analysis, was about 90%.

EXAMPLE 1

A 19-liter reactor was charged with 13,500 g deionized water, 37.8 gKOH, 81 g ammonium perfluoro octanoate (commercially available from 3MCo. as FLUORAD™ FC 143 fluorochemical), 29.8 g Na₂ SO₃, 324 g of a 20%solution of perfluorohexyl sodium sulfinate in water, and a solution of0.56 g CuSO₄.5H₂ O in 500 mL deionized water. After repeatedvacuum/nitrogen purges, the reactor was heated under agitation (375 rpm)to 54° C. and pressurized to 1.93 MPa (280 psig) with a mixture of 95%TFE and 5% propylene. A 10% solution of ammonium persulfate in deionizedwater was fed into the reactor through the use of a constametric pump ata rate of 1.2 grams per minute. As soon as the pressure dropped,indicating polymerization, the monomers were replenished at 1.86 MPa(270 psig), in a ratio of 75% TFE and 25% propylene. The reactionproceeded for 5 hours, during which 4,712 g monomer was consumed to givea calculated average reaction rate of 67 g/l-h. At this time the feed ofammonium persulfate solution was halted, which stopped the reactionwithin 2 minutes. The excess monomer was vented, and a white latex wasdrained from the reactor and the polymer was coagulated by dripping intoa solution of magnesium chloride in water, followed by washing anddrying, to yield a white rubbery polymer. The Mooney viscosity (ML1+10@121° C.) was 71.

EXAMPLE 2

A 19-liter reactor was charged with 14,000 g deionized water, 50 g K₂HPO₄, 9 g KOH, 81 g ammonium perfluoro octanoate, and 324 g of a 20%solution of perfluorohexyl sodium sulfinate in deionized water. Afterrepeated vacuum/nitrogen purges, the reactor was heated to 71° C. underagitation (445 rpm), and pressured to 2.07 MPa (300 psig) with a mixtureof 50% TFE, 5% propylene, and 45% vinylidene fluoride. A 10% solution ofammonium persulfate in deionized water was fed into the reactor using aconstametric pump at a rate of 3 grams per minute. As soon as thepressure dropped, the monomers were replenished with 55% TFE, 15%propylene, and 30% vinylidene fluoride. After 600 g of the ammoniumpersulfate solution was added, this feed was stopped and the reactionallowed to continue. In a total of 7 hours, 3,848 g of monomers wereconsumed to give a calculated average reaction rate of 39 g/l-h. Thereactor was cooled and excess monomer was vented. A white latex wasobtained and was worked up as in Example 1 to yield a rubbery polymerwith a Mooney viscosity (ML 1+10@121° C.) of 28.

EXAMPLE 3

A 150-liter enamel-lined reactor was charged with 105 kg deionizedwater, 2,024 g of a 20% solution of ammonium perfluoro octanoate indeionized water, 284 g KOH, 223 g Na₂ SO₃, 4.2 g CuSO₄.5H₂ O, and 1,472g of a 25% solution of perfluoro butyl sodium sulfinate in deionizedwater. After repeated vacuum/nitrogen purges, the reactor contents wereheated under agitation (210 rpm) to 54° C. and the reactor was pressuredwith a mixture of 84.9% TFE, 12.1% vinylidene fluoride, and 3.0%propylene to a pressure of 1.59 MPa (230 psig). A 10% solution ofammonium persulfate in deionized water was fed to the reactor at a rateof 400 g per hour and as soon as the pressure dropped, the monomer wasreplenished with a mixture of 71% TFE, 22% propylene, and 7% vinylidenefluoride as to maintain a constant pressure of 1.59 MPa (230 psig).After 5.75 hours, a total of 30 kg of monomer was consumed to give acalculated average reaction rate of 50 g/l-h. The initiator feed wasstopped and the excess monomer was vented. The 22.7% solids latex wasdrained from the reactor and the polymer was coagulated by dripping intoa solution of magnesium chloride in water, followed by washing anddrying, to yield a rubbery polymer. The Mooney viscosity (ML 1+10@121°C.) was 90. The number average molecular weight (M_(n)) determined byNMR spectroscopy was 88,000.(0.17 mole % C₄ F₉ end-groups).

EXAMPLE 4

A 150-liter enamel-lined reactor was charged with 105 kg deionizedwater, 2,024 g of a 20% solution of ammonium perfluoro octanoate indeionized water, 68 g KOH, 376 g K₂ HPO₄, and 1,705 g of a 21% solutionof perfluorobutyl sodium sulfinate in deionized water. After repeatedvacuum/nitrogen purges the reactor contents were heated under agitation(210 rpm) to 71 degrees centigrade and the reactor was pressured to 1.59MPa (230 psig) with 83.8% TFE, 3.2% propylene, and 13% vinylidenefluoride. A 10% solution of ammonium persulfate in water was fed to thereactor at a rate of 1.4 kg per hour, and as soon as the pressuredropped, the monomers were replenished with 71% TFE, 22% propylene, and7% vinylidene fluoride as to maintain constant pressure of 1.59 MPa (230psig). After 3.2 kg of the ammonium persulfate solution had been fed,this feed was halted and the reaction was continued. After 5.8 hours, atotal of 30 kg of monomer was consumed to give a calculated averagereaction rate of 49 g/l-h. The reactor was cooled and excess monomer wasvented. The 22.5% solids polymer latex was isolated and worked up as inExample 1. A white rubbery polymer was isolated with a Mooney viscosity(ML 1+10@121° C.) of 65. The number average molecular weight (M_(n))determined by NMR spectroscopy was 91,000 (0.16 mole % C₄ F₉end-groups).

EXAMPLE 5

A 19-liter reactor vessel was charged with 14,000 g deionized water, 50g K₂ HOP₄ buffer, 9 g KOH, 81 g FC-143 emulsifier, and 324 g of a 20%solution of perfluorohexyl sodium sulfinate in water. Under agitation(445 rpm) the reactor was heated to 71° C. and pressurized to 2.00 MPa(290 psig) with a mixture of 95% TFE and 5% propylene. Using aconstametric pump, a 10% solution of ammonium persulfate in water wasfed to the reactor at a rate of 135 g per hour. When the pressuredropped, indicating reaction, the monomers were replenished in a mixtureof 75% TFE and 25% propylene to maintain 2.00 MPa (290 psig). After 389g of the ammonium persulfate solution was added, this feed was stoppedand the reaction continued thermally until a total of 4000 g of monomerwas consumed. This was achieved 4 hours and 45 minutes after thereaction started to give a calculated average reaction rate of 60 g/l-h.At that time, the agitation was decreased and the reactor was cooled andvented. The reactor was drained and a highly transparent latex wasobtained. The latex was coagulated by dripping into a magnesium chloridesolution in water, to yield a snow-white elastomer gum which was washedseveral times with hot deionized water and dried overnight at 110° C.There was obtained a snow-white elastomer gum with a Mooney viscosity(ML 1+10@121° C.) of 25.

COMPARATIVE EXAMPLE 1

Polymer was prepared as in Example 5, but with omission of theperfluorohexyl sodium sulfinate and all the ammonium persulfate wasbatch charged at the beginning instead of pumping it in over time. Thepolymerization was extremely slow and the polymerization was abandonedafter 3 hours. Only 368 g of monomer was consumed over this time to givea calculated average reaction rate of 9 g/l-h.

Comparing Examples 1-5 with Comparative Example C 1 illustrates theeffect of the perfluoro alkyl sulfinate. In Examples 1-5, in whichperfluoro alkyl sulfinate was used, the reaction proceeded rapidly. InComparative Example C 1, even with batch charging the persulfate, therate was much slower than in Examples 1-5. Note that the rate inComparative Example C 1 would have been even slower if the persulfatehad been charged over time as in Examples 1-5, rather than batchcharged.

EXAMPLE 6

A 19-liter vertically-stirred polymerization reactor was charged with14,000 g deionized water, 9 g KOH, 50 g K₂ HPO₄, 81 g ammonium perfluorooctanoate, and 162 g of a 20% solution of C₆ F₁₃ SO₂ Na in deionizedwater. The reactor was then alternately evacuated and purged with N₂until O₂ level is less than 50 ppm. The reactor was then evacuated, thetemperature raised to 71° C., and the agitation set at 445 rpm. Next,the reactor was charged with 455 g of TFE and 8.26 g of propylene togive a pressure of 1.52 MPa (220 psig). The polymerization was initiatedby feeding a 5% solution of (NH₄)₂ S₂ O₈, in deionized water to thereactor by means of a metering pump at approximately 4 g/min until 1equivalent of (NH₄)₂ S₂ O₈ was fed (approximately 370 g of soln.). Uponthe observation of a pressure drop, the running feed, which consisted of93% TFE and 7% propylene, was started and continuously adjusted by thereactor's control system in order to maintain the desired pressure. Thepolymerization was halted by slowing the agitation to 60 rpm after 3,784g of TFE and 278 g of propylene had been fed, 4 hours after start ofrunning feed to give a calculated average reaction rate of 73 g/l-h. Thereactor was then vented, cooled, and drained to isolate the latex. Theresulting polymer was isolated by freeze coagulation, washed six timeswith hot deionized water, and dried overnight in an oven at 100° C. Thepolymer, when analyzed by DSC, exhibited a broad melting transition witha peak melting temperature of 187° C. and a small secondarymelt-transition with a peak melting-temperature of 320° C. whichintegration of the large and small melt-peaks shows accounts for 0.5% ofthe total heat of fusion (see FIG. 1 ). Elemental analysis of thepolymer for carbon, hydrogen, and fluorine, indicated a polymercomposition of 92.3% TFE and 7.7% propylene. The Melt Flow Index (MFI)of the polymer was determined to be 13 g/10 min. @265° C. and 2.5 kgapplied load.

EXAMPLE 7

A 150-liter vertically-stirred polymerization reactor was charged with120,000 g deionized water, 78 g KOH, 430 g K₂ HPO₄, 694 g ammoniumperfluoro octanoate, and 1,023 g of a 20% solution of C₄ F₉ SO₂ Na indeionized water. The reactor was then alternately evacuated and purgedwith N₂ until O₂ level is less than 50 ppm. The reactor was thenevacuated, the temperature raised to 71° C., and the agitation set at210 rpm. Next, the reactor was charged with 3929 g of TFE and 79 g ofpropylene to give a pressure of 15.2 bar (220 psig). The polymerizationwas initiated by feeding a 5% solution of (NH₄)₂ S₂ O₈ in deionizedwater to the reactor by means of a metering pump at approximately 25g/min until 1 equivalent of (NH₄)₂ S₂ O₈ was fed (approximately 3,200 gof solution). Upon the observation of a pressure drop, the running feed,which consisted of 91% TFE and 9% propylene, was started andcontinuously adjusted by the reactor's control system in order tomaintain the desired pressure. The polymerization was halted by slowingthe agitation after 31,300 g of TFE and 3,080 g of propylene had beenfed, 5 hours after start of running feed to give a calculated averagereaction rate of 57 g/l-h. The reactor was then vented, cooled, anddrained to isolate the latex. The resulting polymer was coagulated byadding HCl to the latex, granulated, washed six times with deionizedwater, and dried overnight in an oven at 120° C. The polymer, whenanalyzed by DSC, exhibited a broad melting transition with a peakmelting temperature of 154° C. and a small secondary melt-transitionwith a peak melting-temperature of 316° C. which integration of thelarge and small melt-peaks shows accounts for 2.8% of the total heat offusion (see FIG. 2). Elemental analysis of the polymer for carbon,hydrogen, and fluorine, indicated a polymer composition of 90.9% TFE and9.1% propylene. The Melt Flow Index (MFI) of the polymer was determinedto be 3.3 g/10 min. @265° C. and 2.16 kg applied load.

EXAMPLE 8

An 86-liter vertically-stirred polymerization reactor was charged with52,000 g deionized water, 140 g KOH, 300 g ammonium perfluoro octanoate,110 g Na₂ SO₃, 2 g CuSO₄.5H₂ O, and 1,000 g of a 20% solution of C₆ F₁₃SO₂ Na in deionized water. The reactor was then alternately evacuatedand purged with N₂ until O₂ level is less than 50 ppm. The reactor wasthen evacuated, the temperature raised to 54° C., and the agitation setat 150 rpm. Next, the reactor was charged with 1256 g of TFE and 37.18 gof propylene to give a pressure of 0.83 MPa (120 psig). Thepolymerization was initiated by feeding a 10% solution of (NH₄)₂ S₂ O₈,in deionized water to the reactor by means of a metering pump atapproximately 3 g/min until 778 g of soln. was fed. Upon the observationof a pressure drop, the running feed, which consisted of 88% TFE and 12%propylene, was started and continuously adjusted by the reactor'scontrol system in order to maintain the desired pressure. Thepolymerization was halted by slowing the agitation to 30 rpm after 7,825g of TFE and 1080 g of propylene had been fed, 5 hours after start ofrunning feed to give a calculated average reaction rate of 34 g/l-h. Thereactor was then vented, cooled, and drained to isolate the latex. Theresulting polymer was isolated by freeze coagulation, washed six timeswith hot deionized water, and dried overnight in an oven at 100° C. Thepolymer, when analyzed by DSC, exhibited a broad melting transition witha peak melting temperature of 103° C. and no secondary melt-transitionabove 300° C. (see FIG. 3). Elemental analysis of the polymer forcarbon, hydrogen, and fluorine, indicated a polymer composition of 88.1%TFE and 11.9% propylene. The Melt Flow Index (MFI) of the polymer wasdetermined to be 7 g/10 min. @190° C. and 2.5 kg applied load.

COMPARATIVE EXAMPLE C2

A 19-liter vertically-stirred polymerization reactor was charged with14,000 g deionized water, 9 g KOH, 50 g K₂ HOP₄, and 81 g ammoniumperfluoro octanoate. The reactor was then alternately evacuated andpurged with N₂ until O₂ level is less than 50 ppm. The reactor was thenevacuated, the temperature raised to 71° C., and the agitation set at445 rpm. Next, the reactor was charged with 414 g of TFE and 11.2 g ofpropylene to give a pressure of 1.59 MPa (230 psig). The polymerizationwas initiated by feeding a 5% solution of (NH₄)₂ S₂ O₈ in deionizedwater to the reactor by means of a metering pump approximately 14 g/minuntil 1 equivalent of (NH₄)S₂ O₈ was fed (approximately 370g of soln.).No pressure drop, which would indicate the onset of polymerization, wasobserved.

COMPARATIVE EXAMPLE C3

Following the procedure of example 6 of U.S. Pat. No. 3,933,733, supra,an 86-liter vertically-stirred polymerization reactor was charged with60,000 g deionized water, 300 g NaOH, 300 g ammonium perfluorooctanoate, and 12 g Na₂ SO₃. The reactor was then alternately evacuatedand purged with N₂ until O₂ level is less than 50 ppm. The reactor wasthen evacuated, the temperature raised to 60° C., and the agitation setat 150 rpm. Next, the reactor was charged with 2100 g of TFE and 46.5 gof propylene to give a pressure of 1.72 MPa (250 psig). Thepolymerization was initiated by feeding a 5.7% solution of (NH₄)₂ S₂ O₈in deionized water to the reactor by means of a metering pump at maximumpump speed (approximately 100 g/min) until 432 g of soln. was fed. Uponthe observation of a pressure drop, the running feed, which consisted of88% TFE and 12% propylene, was started and continuously adjusted by thereactor's control system in order to maintain the desired pressure. Thepolymerization was halted after 6 hours by slowing the agitation to 50rpm, during which time 3,458 g of TFE and 489.5 g of propylene had beenfed to give a calculated average reaction rate of 11 g/l-h. The reactorwas then vented, cooled, and drained to isolate the 6% solids latex. Theresulting polymer was isolated by freeze coagulation, washed six timeswith deionized water, and dried overnight in an oven at 100° C. Thepolymer, when analyzed by DSC, exhibited two melting transitions withpeak melting temperatures of 105° C. and 316° C. (see FIG. 4).Integration of the large and small melt-peaks shows that 26% of thetotal heat of fusion is attributable to the 316° C. peak (See FIG. 4).Elemental analysis of the polymer for carbon, hydrogen, and fluorine,indicated a polymer composition of 88.1% TFE and 11.9% propylene. TheMelt Flow Index (MFI) of the polymer was determined to be zero g/10min@265° C. and 15 kg applied load.

COMPARATIVE EXAMPLE C4

Following the procedure described in U.S. Pat. No. 4,463,144, supra,except using ammonium perfluoro octanoate as the emulsifier, an 86-litervertically-stirred polymerization reactor was charged with 51,600 gdeionized water, 5,600 g t-butanol, 281 g ammonium perfluoro octanoate,167 g KOH, 857 g K₂ HPO₄, 3.4 g Na₂ EDTA, and 2.8 g FeSO₄.7H₂ O. Thereactor was then alternately evacuated and purged with N₂ until O₂ levelis less than 50 ppm. The reactor was then evacuated, the temperatureraised to 27° C., and the agitation set at 130 rpm. Next, the reactorwas charged with 2170 g of TFE and 64.1 g of propylene to give apressure of 1.52 MPa (220 psig). The polymerization was initiated byfeeding a solution consisting of 175 g ⁺ Na⁻ SO₂ CH₂ OH, 15 g Na₂ EDTA,and 18.4 g KOH in 1810 g of deionized water, to the reactor by means ofa metering pump (approximately 3 g/min) until 950 g of soln. was fed.Upon the observation of a pressure drop, the running feed, whichconsisted of 88% TFE and 12% propylene, was started and continuouslyadjusted by the reactor's control system in order to maintain thedesired pressure. The polymerization halted after 8,479 g of TFE and1,173 g of propylene had been fed, 5.5 hours after start of running feedto give a calculated average reaction rate of 30 g/l-h. The reactor wasthen vented, cooled, and drained to isolate the polymer suspension. Theresulting polymer was isolated by filtration, washed six times with hotdeionized water, and dried overnight in an oven at 100° C. The polymer,when analyzed by DSC, exhibited two melting transitions with peakmelting temperatures of 114° C. and 321° C. (see FIG. 5). Integration ofthe large and small melt-peaks shows that 27% of the total heat offusion is attributable to the 321° C. peak (see FIG. 4). Elementalanalysis of the polymer for carbon, hydrogen, and fluorine, indicated apolymer composition of 88.8% TFE and 11.2% propylene. The Melt FlowIndex (MFI) of the polymer was determined to be 59 g/10 min@265° C. and5 kg applied load.

Examples 6-8 and Comparative Examples C2 and C3 show that unlike thesemi-crystalline polymers of the prior art, the semi-crystallinepolymers of this invention have very little if any melt transitionsabove 300° C. It is believed that the improved melt-processing ofsemi-crystalline polymers of this invention is due in part to theabsence of significant melt-transitions above 300° C.

FT-IR spectra of thin films of the resulting polymers showed noobservable carbonyl absorptions for Examples 6-9, a relatively largecarbonyl absorption at 1695 cm⁻¹ for Comparative Example C2, and amoderate carbonyl absorption at 1744 cm⁻¹ for Comparative Example C3.This indicates that the polymers of this invention do not containsignificant amounts of carbonyl-containing end-groups.

Various modifications and alterations of this invention will be apparentto those skilled in the art without departing from the scope and spiritof this invention and this invention should not be restricted to thatset forth herein for illustrative purposes.

What is claimed is:
 1. A semi-crystalline polymer comprisinginterpolymerized units derived from tetrafluoroethylene andallylic-hydrogen containing olefin monomer, wherein less than 10% of thetotal heat of fusion is attributable to a secondary melt-transitionabove 300° C. as shown by the heating curve from Differential ScanningCalorimetry.
 2. The polymer of claim 1 wherein less than 5%, of thetotal heat of fusion is attributable to a secondary melt-transitionabove 300° C. as shown by the heating curve from Differential ScanningCalorimetry.
 3. The polymer of claim 1 wherein said allylic-hydrogencontaining olefin monomer is a mono-olefin consisting of carbon,hydrogen, and halogen atoms.
 4. The polymer of claim 1 wherein saidallylic-hydrogen containing olefin monomer is selected from the groupconsisting of propylene, butylene, isobutylene, and1,1,2-trifluoropropene.
 5. The polymer of claim 1 wherein saidallylic-hydrogen containing olefin monomer is propylene.
 6. The polymerof claim 1 wherein said polymer consists essentially of interpolymerizedunits derived from tetrafluoroethylene and allylic-hydrogen containingolefin monomer.
 7. The polymer of claim 1 wherein said polymer consistsessentially of interpolymerized units derived fromethylenically-unsaturated monomers.
 8. The polymer of claim 1 whereinsaid polymer consists essentially of interpolymerized units derived fromtetrafluoroethylene and allylic-hydrogen containing olefin monomers. 9.Shaped article comprising the polymer of claim 1.